In the industry, the hydrolysis of starch starts mainly with α-amylase. The synergistic application of these α-amylases derived from microorganisms and other enzyme species, such as pullulanase, glucoamylase and glucose isomerase, can effectively break down starch macromolecules, and the produced small-molecule polysaccharides or monosaccharides have many applications in food manufacturing, grain processing, beer processing, and alcohol production. The α-amylase belongs to one kind of saccharifying hydrolase, with a main structural feature of (α/β) 8 folding, which contains a special starch substrate binding site with a length of generally no more than 10 saccharide monomers. However, the binding sites of several amylases can work together to perform multi-site binding to successfully cleave starch macromolecules.
The α-amylase can effectively cleave α-1,4 glycosidic bond in the starch substrate, thereby rapidly reducing molecular weight and viscosity of the starch substrate, with the products being mainly dextrins of different lengths. There are different kinds of α-amylases, and industrial application conditions of these kinds of α-amylases vary greatly depending on the characteristics of the desired products.
The α-amylase (α-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) is effective in hydrolyzing α-1,4 glycosidic bond in starch and other polysaccharides. In view of the demand for improving enzyme efficiency and reducing production cost during the hydrolysis of starch, the search for α-amylase which can support effective starch liquefaction in different application fields has become an important research direction in the academia and industry. At present, the improvements of the enzyme species by using enzyme engineering techniques mainly focus on the improvements of heat resistance, acid-base tolerance performance, and liquefaction effect.
Many α-amylases in plants and microorganisms have been found to have commercial values, mainly including B. licheniformis α-amylase, B. amyloliquefaciens α-amylase and G. stearothermophilus α-amylase, wherein the variants derived from B. licheniformis α-amylase (L-type) as a template are the most abundant and are most widely used.